Automated Material Handling Systems (AMHS) have been widely used in semiconductor fabrication facilities (“FABS”) to automatically handle and transport groups or lots of wafers between various processing machines (“tools”) used in chip manufacturing. A typical FAB may include one or more floors having a plurality of process bays including processing tools and wafer staging equipment which are interconnected by the AMHS.
Each bay may include a wafer stocker, which includes multiple bins for temporarily holding and staging a plurality of wafer carriers during the fabrication process. The wafer carriers may include standard mechanical interface (SMIF) pods which may hold a plurality of 200 mm (8 inch) wafers, or front opening unified pods (FOUPs) which may hold larger 300 mm (12 inch) wafers. Stockers generally include a single mast robotic lift or crane having a weight bearing capacity sufficient for lifting, inserting, and retrieving a single wafer carriers at one time from the bins. The stocker holds multiple SMIF pods or FOUPs in preparation for transporting a SMIF or FOUP to the loadport of a processing tool.
A semiconductor FAB may include numerous types of automated and manual vehicles for moving and transporting wafer carriers throughout the FAB during the manufacturing process. These may include for example automatic guided vehicles (AGVs), personal guided vehicles (PGVs), rail guided vehicles (RGVs), overhead shuttles (OHSs), and overhead hoist transports (OHTs). An OHT system automatically moves OHT “vehicles” that carry and transport wafer carriers, such as SMIF pods or FOUPs holding multiple wafers, from a processing or metrology tool or a stocker to the loadport of another tool or other apparatus in the FAB. The OHT system may be used to transport vehicles within each bay (intra-bay) or between bays (inter-bay). The OHT system also moves empty vehicles (i.e. without a wafer carrier) to the tool loadport or other apparatus for receiving and removing empty or full SMIF pods or FOUPs that may contain wafers for further transport and/or processing in other tools.
Handling and transport of 300 mm wafers in correspondingly larger and heavier FOUPS creates efficiency challenges for the AMHS to maintain expedient wafer flow between processing tools in the semiconductor FAB. In addition, construction of large “Giga FABS” with potential capacities to handle processing of more 100,000-300 mm wafers per month creates additional demands. These challenges and demands include efficient use of floor and overhead space in the FAB, handling increased transportation volumes of FOUPs, reducing wafer transport system bottlenecks at various process choke points that create wafer carrier vehicle “traffic jams,” and expedient intra-bay and inter-bay FOUP transportation including cross-floor (i.e. between floor) transport of FOUPS between multiple floors in a Giga FAB.
An improved system and method for handling wafer transport in a semiconductor FAB is desired.
All drawings are schematic and are not drawn to scale.